Connection system foe



Jan. 24, 139. K. SCHLESINGER' CONNECTION SYSTEM FOR TELEVISION TUBES Filed Feb. 9, 1935 Patented Jan. 24, 1939 UNHTED ST'E'EE cries TUBE Kurt Schlesinger, Berlin, Germany, assignor to Radioaktiengesellschaft D. S. Loewe, Berlin- Steglitz, Germany Application February 9, 1935, Serial No. 5,871 In Germany February 12, 1934 3 Claims.

Modern television tubes, when operated from an A. C. mains supply, require a very perfect ripple-elimination. The filter chains necessary for this purpose possess, however, very long periods of charge and discharge. In consequence the necessary operating potentials do not occur immediately after switching-on has been initiated, and the output potentials are formed during a relatively long period. These may be very dangerous to the television tube, particularly in the case of the gas-filled type. In accordance with the invention this requirement is combined with the requirement for ripple elimination.

The present invention relates to arrangements which enable a very perfect ripple elimination without any drawback,

The invention will be described in connection with the annexed drawing, in which Fig. 1 shows for example an arrangement acaccording to the invention,

Fig. 2 shows the course of the connection and disconnection potential curves, while in Fig. 3 there is illustrated an improved connection according to the present invention.

In Fig. 1 the transformer l of the mains-connection apparatus is connected with the mains 3 through the medium of a switch 2, and transforms to an alternating potential of approximately 2000 volts peak value. Half-wave rectification in the tube t in conjunction with a condenser 5 provides wholly inadequate ripple elimination. It is necessary, therefore, to provide a further ripple elimination for the cathode potential by a resistance 6 and condenser l. The cathode 8 of the television tube I6 is directly connected with the condenser l, whilst the control electrode 5 is connected to the cathode through the medium of a leak resistance It with a somewhat more negative point of the connection system, viz, a tapping at the steadying resistance 6, and through the medium of the condenser II to the output potential of the television receiver I2. The anode 23 of the television tube It is connected with earth I3.

may be regarded as typical for all mains-connection systems for television tubes of this kind. The connections between receiver and deflection means of the tube are not shown.

At switching in the apparatus the negative potential, which proceeds from the rectifier tube 4, is built up more quickly at the cathode 8 than at the control grid 9. The rate at which the cathode is charged is determined by the time constant of the combination of resistance 5 and condenser 1. Charging the control grid, however,

This connection systemrequires a longer time, as this grid is connected through the medium of an additional resistancecondenser combination IO, N with the receiver 52, and over the low resistance of the latter with earth. The result of this is a course of the connection and disconnection curves as illustrated in Fi 2. In Fig. 2 ordinates represent the potential diiference between the cathode 8 or control rid 9 and the earthed anode 20, and abscissae the time t after the moment of switching in. 10 Both curves will be approximately exponential, but the switching-in curve of the cathode, designated l4, reaches the cathode bias, viz., the potential value it, earlier than the grid electrode 9, the corresponding curve of which is repre- 15 sented by the line Hi. In consequence the relative potential between the grid and the cathode within the shaded zone up to the point of intersection P is positive, the same reaching a value 5? dangerous to the tube and amounting to more 20 than 100 volts shortly after switching in. In this connection break-downs may occur resulting in destruction of the television tube. Also in the case of high-vacuum tubes, since the cathode has not yet become properly heated, there may occur a 25 spot-like heating of the oxide and accordingly damage to the cathode, particularly in the case of frequent repetition of the switching-in operation.

It is not until the time abscissa belonging to the point P has been exceeded that the control grid 30 9 becomes negative in relation to the cathode 8 and finally reaches the correct negative potential value H8.

The processes occurring at the disconnection are illustrated by the curves l4 and I1, and 35 show that in this connection the bias always remains negative, so that the tube is accordingly out of danger.

A satisfactory practical solution to the problem is accordingly obtained if in accordance with 40 the invention the time constant of the control grid circuit is made equal to or preferably less than that of the cathode circuit. There are then obtained the charging and discharging curves l4 and I?" shown in broken lines, I4 being the 45 cathode curves, II" the grid curves. These curves show, however, that upon the disconnection the curves might again intersect at the point Q. If the grid possesses a much smaller time constant than the cathode, there again occurs a positive 5 grid bias beyond Q. This, however, is not very dangerous, as all potentials, including the anode potential, have then considerably dropped.

The possibility of performing the inventive idea in simple fashion is revealed by observation of Fig. 1 from the fact that the resistance and condenser combination 6, 1 requires to be a filter chain for ripple in the mains, and accordingly possesses of necessity a time constant, which is much greater than 50 periods. On the contrary the circuit ll, ll! should allow passage only to frequencies higher than the image-change frequency of 25 periods. The time constant I0, I I may accordingly be made between and A of that of 5, I, so that the difference in the resulting time constants of the circuits at the control grid 9 and cathode 8 is extremely small.

dimensioning in practice is as follows:

Resistance 6:0.3-10 ohms. Condenser 7:0.3 mf. Resistance I0=0.3- 10 ohms. Condenser ll=0.011 mf.

The time constant of the latter circuit then amounts to merely approximately ,5 of that of the former. The impedance of H nevertheless remains even for 25 periods in the same order of magnitude as that of in, but does not produce any deterioration of the image in view of the phase difference in relation to ID.

Regarding the ripple elimination in the stationary condition of the receiver the control grid 9 is more completely steadied than the cathode 8, as the ripple elimination of 8 is effected only by the condenser 6 and resistance 1, whilst the bias for electrode 9 is additionally steadied by 10/. If, therefore, complete smoothness against earth is assumed to exist in respect of the control grid 9, an interfering frequency will nevertheless occurinthe image (in the form of two black transverse stripes corresponding to 25periods), as a relative humming potential difference exists between grid 9 and cathode 8.

Accordingly a perfect ripple elimination .of the cathode point Bcan be obtainedbut with difliculty. In the case of control in view of 10 volts grid potential and with the great sensitiveness of the eye to variations in the intensity of the light in. theimage. the relative :humming potential .between grid and cathode should be smaller than one-tenth of the maximum video potential, i. e., less than 1 volt, preferably not more than 0.1 volt. In order to obtain this it wouldbe necessary to perform the steadying of the cathode potential of say 2000 volts to an extent of approximately l0 owing to the fact that the. ripple potentials 9 and it have thesame potential.

When, for improvement of the smoothing, 6 would be increased too much anode potential would'be lost and a very expensive high-tension transformer I would be required; inthe case of increasing, the costs of this high-tension condenser would become too high. Withcapacities 5, l of approximately 0.5 mf., which represent the extreme limit in practice and already require a relatively large amount of space, and with a resistance 6 of 0.3 megohm, it is impossible to obtain a ripple elimination better than 1/20.

According to the invention the effect of the ripple is eliminated by conveying to the grid 9, the ripple of the cathode in exactly the same intensity and phase.

The connection system according to Fig. 1 represents upon closer inspection a bridge connection, the'one branch of which consists of 6 and l and the other branch of i0 and II, the cathode 8 being connected'with the corner of the first branch and the grid 9 with the corner of the sec-- ond branch.

A possible (R ll (10 ohms) (Cg H (mf.)

0.05 megohm 0.25 mf. .5 megohm .03 mf. 1 megohm 0.015 mf.

These values apply with:

6:0.25 up to .05 megohm 1:0.25 mf.

The arrangement according to the invention obviously has the advantage that steadying means, which are cheap because they are small, may be employed.

The stated arrangement enables the stripes in the image caused by the humming to be completely avoided; there remains however, another defect in the image owing to extensive formation of veils.

Thisas the applicant has foundis due to the fact that the time constant I 0/ H is too small. With respect to the lower video frequencies it should amount to at least sec., but if possible should be even greater. The time constant of the circuit described, however, amounts to only of this value.

To avoid said defect, the scheme of Fig. 1 is improvedaccording to that of Fig. 3. It differs fromv that of Fig, 1 by a resistance 25 connecting the tapping point of resistance 6 to the variable resistance In and, through condenser 24, to the anode of 4.

The arrangement has the following object: By reason of the bridging condenser 24 it is intended to transmitto the control grid 9 the maximum humming potential occurring in the connection, i. e. at the anode of the rectifier tube 4 in full amount, that is to say,whilst avoiding the bypath through 6/1. The capacity of 2 should be at least 0.1 mf., better 0.5 mf.; it is subject to A. C. potential only and is accordingly cheap. The resistance 25 should be large as compared with the A. C. resistance of 24 and may amount to 0.3 or 0.5 megohm. The humming potential at the point 26 between 24 and I0 is now as many times greater than before as the direct voltage division at 6, with the stated dimensions about 6 times greater; In order now to compensate this the proportion of the branch iil/ H must accordingly be reduced. This, however, means nothing else than'that by increasing It] or I i or both together, the time constant of this circuit is to be made six times greater. The practical values are in fact i=2 megohms, H=0.033 mf. corresponding with a time constant of approximately 0.06 sec. The resistance 23 serves for facilitating the adjustment of the bridge. This way ripple and veil formation are eliminated simultaneously.

I claim:

1. In a television receiver including an earthed radio receiver, a cathode ray tube having cathode, control grid and earthed anode and a mains supply apparatus comprising a transformer, a single rectifier tube and smoothing means, said smoothing means consisting of a first condenser connecting the anode of said rectifier tube to earth, a resistance connecting the same anode to the cathode of said cathode ray tube and a second condenser connecting said cathode to earth, said control grid connected by a third condenser to said receiver and by a leak resistance to a slider on said resistance: the discharge time constant of said control grid circuit being at most equal to that of said cathode circuit.

2. In a television receiver including an earthed radio receiver, a cathode ray tube having cathode, control grid and earthed anode and a mains supply apparatus comprising a transformer, a single rectifier tube and smoothing means, said smoothing means consisting of a first condenser connecting the anode of said rectifier tube to earth, a resistance connecting the same anode to the oathode of said cathode ray tube and a second condenser connecting said cathode to earth, said control grid connected by a third condenser to said receiver and by a leak resistance to a slider on said resistance: the discharge time constant of said control grid circuit being at most equal to that of said cathode circuit, means being provided to eliminate the efiect of the ripple on the ray of said cathode ray tube by conveying to cathode and control grid of said tube a ripple equal in amplitude and phase.

3. In a television receiver including an earthed radio receiver, a cathode ray tube having cathode, control grid and earthed anode and a mains supply apparatus comprising a transformer, a single rectifier tube and smoothing means, said smoothing means consisting of a first condenser connecting the anode of said rectifier tube to earth, a resistance connecting the same anode to the oathode of said cathode ray tube and a second condenser connecting said cathode to earth, said control grid connected by a third condenser to said receiver and by a leak resistance to a slider on said resistance: the discharge time constant of said control grid circuit being at most equal to that of said cathode circuit, means being provided to eliminate the efiect of the ripple on the ray of said cathode ray tube by conveying to cathode and control grid of said tube a ripple equal in amplitude and phase, said means consisting of a resistance connecting said leak resistance to the slider of said first resistance and a condenser connecting the same terminal of said leak resistance to the anode of said valve.

KURT SCI-ILESINGER. 

